The invention disclosed is a method and an apparatus for measuring distance between a slider and a transparent disk with sub-nanometer resolution, particularly in nanometer flying height measurement of a read-write head on a glide disk by applying ellipsometry.
According to the prior art, the methods for measuring thickness of an air film, e.g. flying height of a slider, are generally classified into a) capacitance type, b) light interferometry, and c) ellipsometry with fixed incident angle. The capacitance type is used to measure flying information of a slider. Three unshielded capacitance probes are mounted on the slider for monitoring the roll angle, the pitch angle, and the flying height of the slider. However, the measured signal intensity is inversely proportional to the flying height of the slider. Besides, the slider for measuring the flying height by using this method must be made of special materials, e.g. ceramics, and the cost is high. Therefore, the capacitance type is nowadays out of date. Generally, the flying height measured by using this method is limited ranging from 1000 nm to 5000 nm.
Owing to different light beam sources, different methods, e.g. laser beam interferometry or white light interferometry, for measuring the flying height of a slider by applying interferometry are developed. The method for measuring the flying height of a slider by applying laser beam interferometry is published by Best et. al. on pp. 1017-1018, No. 5, Vol. MAG-22, IEEE Transaction On Magnetics in 1986. The monochrome is used as the light source. The phase difference of the incident light toward the slider and the reflected light from the slider is 180 degrees. Because of interference of the incident light and the reflected light, the flying height of the slider can be obtained according to the counted changes of the interference fringes. However, the accuracy of the counted changes of the interference fringes is not high. Moreover, the slider is assumed being made of dielectric material. Therefore, the absorption coefficient of the slider is neglected, and the neglected absorption coefficient thus results in great deviation of the measured flying height of the slider. With respect to the white light interferometry, the interference fringes are analyzed by using a spectrum meter. The two wavelengths of the corresponding maximum light intensity and the corresponding weakest light intensity are obtained for determining the flying height of a slider. The flying height measured by using this method is limited ranging from 127 nm to 750 nm. Once the distance between the slider and the disk is less than 127 nm, there are no apparent peaks and valleys of the interfering light intensity for the interference fringes to determine the flying height of the slider. As for the dynamic interferometry developed by the Phase Metrics Company, the change of the flying height is more than a quarter of the wavelength for obtaining the curves of the corresponding movements for the continuous changes of the maximum light intensity and the weakest light intensity. The curves are used for calibration before the flying height is measured. For example, Ohkuboy developed a system for measuring the flying height of a slider by using the Hexe2x80x94Ne laser as the light source. The fringe orders are obtained according to the variations of the interfering light intensities while the slider lands on the disk for being used for calibration before measuring the flying height. In 1992, C. Lacey disclosed to use the mercury arc lamp, which primarily incident the light beam with wavelengths of 436 nm, 548 nm and 580 nm, as the interfering light source. The calibrating curve is obtained while the magnetic head is unloaded from the disk by the rotating arm.
Generally, the laser Doppler Vibrometer/Interferometry (LDV/I) is used to determine the dynamic actions of the suspension systems for a slider of a hard disk. T. C. McMillan and F. E. Talke uses three wavelengths laser beam as the interfering light source in 1994 for measuring the flying height of a slider (pp. 1017-1018, No. 5, Vol. MAG-22, IEEE Transaction On Magnetics). The intensities of the interference fringes are determined by the method of interpolation, where the maximum light intensity and the obtained weakest light intensity are obtained first. The flying height of a slider less than 100 nm is measured by phase demodulation. The method for measuring the flying height of a slider by applying laser beam division interferometry is published by C. K. Lee and T. W. Wu on pp. 1675-1680, No. 9, Vol. 33, AIAA Journal in 1995. One laser beam is projected onto the back of the slider to determine the dynamic characteristic thereof, while the other is projected onto the surface of the disk to determine the dynamic contact point in real time to modify deviation for obtaining higher accuracy. M. Staudenmann, M. J. Donovan and D. B. Bogy disclosed a method for measuring the flying height of a slider on pp. 4173-4175, No. 6, Vol. 30, IEEE Transaction in 1998. The laser beam is projected onto the back of the slider. By comparing the incident laser beam with the reflected laser beam from the slider, the velocity of the slider is obtained by frequency demodulation, and the movement of the slider is obtained by phase demodulation. However, according to this method, the magnetic head must be landed on the disk or a laser beam must be divided onto the surface of the disk for being used as reference light beam for the contact point. Beside, because the obtained flying height is the distance between the slider and the glide disk, deviation of the flying height rises owing to the dynamic actions of the slider and the distance variation.
In recent years, the flying height tends to be much lower because of increase of the coding density of a hard disk. For the present, the flying height is less than 25 nm, therefore more accurate measurement is expectable required. Phase Matrics Company and Zygo Company both disclosed that the flying height of a slider and the optical properties of the surface of the slider can be obtained by applying ellipsometry. C. Lacey assumes that the complex refraction index all over the slider are all the same, therefore the flying height and the complex refraction index values of the slider can be obtained by using a imaging ellipsometer. In his setup, a charge-coupled device (CCD) is used, and the ellipsometric information of multiple points can be obtained without further unloading the slider to vary its flying height. Therefore, the flying height of the slider can be obtained according to the pitch, roll, crown, cross-crown and twist parameters. The essential assumption in the method is that the slider is made of pure substrate regardless of thin films. However, it""s not the case. Besides, the variation of the complex refraction index of the slider surface is not negligible for measuring the flying height. In 1996, Peter de Groot discloses how to obtain the complex refraction index of the magnetic by applying ellipsometry with fixed incident angle (U.S. Pat. No. 5,557,399). Please refer to FIG. 1, a schematic diagram of the conventional system for the flying height measurement, which is modeled as an air film 302, of a slider 301 by applying ellipsometry with fixed incident angle. In each measurement of the flying height of the slider, the slider 301 is loaded first, and moved from the distance over one wavelength to the distance less than one wavelength. The vertical and horizontal light intensities and the maximum and minimum values of the phase are measured for the first step, therefore the flying height d and the complex refraction indexes n, k values of the slider can be solved through the ellipsometry.
From 1995, it""s well known that the magneto-impedance read-write head (MR head) is generally used as the read-write head of a hard disk. For improving read-write performance and increasing storing density, the flying height of the magneto-impedance read-write head (MR head) is generally set to be lower than 25 nm. Moreover, because the magneto-impedance read-write head (MR head) is sensitive to electrical field, a film made of diamond like carbon (DLC) being in a thickness of about 12 nm is generally coated on the surface of the magneto-impedance read-write head (MR head) by sputtering. Therefore, in order to obtain the surface property of the coated film with high reflectivity, an apparatus with resolution higher than 12 nm for measuring the flying height is needed. On the other hand, as for near-field optical storage technique, a slider of the hard disk with nanometer resolution is presently used as a loading stage to load an optical head. Therefore, it""s important to focus on how to accurately measure the flying height of a loading stage applied in the near-field optical storage technique.
According to ellipsometry, the flying height of a slider is obtained by measuring the light intensity and the phase information of the light. The principle for measuring the flying height of a slider is described briefly as follows.
The electrical field of a planar wave can be decomposed into two orthogonal polarization components p wave and s wave in the vector form
{right arrow over (E)}={right arrow over (E)}p+{right arrow over (E)}sxe2x80x83xe2x80x83(1)
which is further expressed in the Jone""s matrix as follows                               E          ⇀                =                              [                                                                                E                    p                                                                                                                    E                    s                                                                        ]                    =                                    [                                                                                                                  E                        op                                            ⁢                                              ⅇ                                                  j                          ⁡                                                      (                                                                                          ω                                ⁢                                                                  xe2x80x83                                                                ⁢                                t                                                            -                              kz                              +                                                              φ                                p                                                                                      )                                                                                                                                                                                                                                  E                        os                                            ⁢                                              ⅇ                                                  j                          ⁡                                                      (                                                                                          ω                                ⁢                                                                  xe2x80x83                                                                ⁢                                t                                                            -                              kz                              +                                                              φ                                s                                                                                      )                                                                                                                                                          ]                        ∝                          [                                                                                                                  E                        op                                            ⁢                                              ⅇ                                                  j                          ⁢                                                      xe2x80x83                                                    ⁢                          Δ                                                                                                                                                                                E                      os                                                                                  ]                                                          (        2        )            
where xcex94=xcfx86pxe2x88x92xcfx86s, Eop and Eos are the respective electrical field amplitudes of the p wave and s wave, and the light beam transmits along the z axis. If the respective input polarization electrical fields of the p wave and s wave are Eip and Eis, and the respective output polarization electrical fields of that through a sample are Erp and Ers, the respective reflection coefficients of the p wave and s wave are                               r          p                =                                            E              rp                                      E              ip                                =                                    ρ              p                        ⁢                          ⅇ                              j                ⁢                                  xe2x80x83                                ⁢                                  Δ                  p                                                                                        (        3        )                                          r          s                =                                            E              rs                                      E              is                                =                                    ρ              s                        ⁢                          ⅇ                              j                ⁢                                  xe2x80x83                                ⁢                                  Δ                  s                                                                                        (        4        )            
where xcex94p is the phase shift of the reflected p wave, and xcex94s is the phase shift of the reflected s wave. The polarization transfer function F (ellipsometric function xcfx81) is thus defined as                     F        =                  ρ          =                                                                      E                  rp                                                  E                  rs                                                                              E                  ip                                                  E                  is                                                      =                                                                                E                    rp                                                        E                    ip                                                                                        E                    rs                                                        E                    is                                                              =                                                                    r                    p                                                        r                    s                                                  =                                                                                                    ρ                        p                                            ⁢                                              ⅇ                                                  j                          ⁢                                                      xe2x80x83                                                    ⁢                                                      Δ                            p                                                                                                                                                              ρ                        s                                            ⁢                                              ⅇ                                                  j                          ⁢                                                      xe2x80x83                                                    ⁢                                                      Δ                            s                                                                                                                                =                                      tan                    ⁢                                          xe2x80x83                                        ⁢                                          Ψⅇ                                              j                        ⁢                                                  xe2x80x83                                                ⁢                        Δ                                                                                                                                                    (        5        )            
where       tan    ⁢          xe2x80x83        ⁢    Ψ    =            ρ      p              ρ      s      
and xcex94=xcex94pxe2x88x92xcex94s are ellipsometric parameters.
Please refer to FIG. 2, which is a schematic diagram showing an system configuration of a PMSA ellipsometer (P: the polarizer, M: the phase modulator, S: the sampler, and A: the analyzer). Every component can be expressed in a Jone""s Matrix and the variation of the light beam can be described by the parameters. If the photo detector possesses linear correspondence, the measured signal behind the analyzer can be expressed as
I=G{right arrow over (E)}out+{right arrow over (E)}out=G(ASMP{right arrow over (E)}in)+(ASMP{right arrow over (E)}in)xe2x80x83xe2x80x83(6)
Expression (10) can be expressed as
I(xcex4)=G[I+Ip sin(xcex4)+Is cos(xcex4)]xe2x80x83xe2x80x83(7)
From the sensitivity of the photo detector, the linear circuit amplification and the ellipsometric parameters, the constant G can be determined. If phase of incident light beam is modulated, it is to be solved by a lock-in amplifier circuits and the ellipsometric parameters xcexa8 and xcex94 will be further obtained.
An object of the present invention is to provide a method and an apparatus for measuring the flying height of a slider with sub-nanometer resolution.
According to the first aspect of the present invention, the present invention is related to a method for measuring a distance between a sliding object and a transparent disk with sub-nanometer resolution, wherein the distance is regarded as a nanometer specimen, at least comprising steps of a) providing a sampling light beam with adjustable initial polarization state by phase modulation, and with variable incident angles, which is controlled by an optical control subsystem, relative to the air film and forming a first reflected light beam of the sampling light beam relative to the air film, b) guiding the first reflected light beam of the sampling light beam through the optical control subsystem to form a return light beam traveling in the opposite direction to the first reflected light beam, wherein the return light beam being incident to the specimen again at the the detecting site, therefore a second reflected light beam of the returned light beam is formed, while the second reflected light beam exits from the the optical control subsystem in the opposite direction to the the sampling light beam, it is to form a signal light beam, c) guiding the signal light beam through the analyzer and the detectors for detection of intensity and phase change of the signal light beam, and d) partially dividing the signal light beam to form a observing light beam, which is guided to a microscope and used as a light source for observation of the detecting site on the the specimen.
Preferably, the transparent disk is a glass disk.
Preferably, the distance is to be measured less than one wavelength of the linear polarizing light.
Preferably, the slider is made of non-dielectric material.
Preferably, the slider is in static state relative to the transparent disk while the sampling light beam is incident onto a surface of the slider.
Preferably, the slider is in motion relative to the transparent disk while the sampling light beam is incident onto a surface of the slider.
Preferably, the incident light beam of the return light beam exits from the optical control subsystem to becomes a signal light beam traveling along the same path but in the opposite direction to the sampling light beam and at least twice reflecting from the detecting site.
Preferably, the observing light beam is used for the microscope as a light source of observation on detecting site as well as for the auto-collimation of the sampling light beam.
According to the second aspect of the present invention, the present invention is related to a method for measuring a distance between a sliding object and a transparent disk with sub-nanometer resolution, wherein the distance is regarded as a nanometer specimen, at least comprising steps of a) providing a sampling light beam with adjustable initial polarization state by phase modulation, and with variable incident angles, which is controlled by an optical control subsystem, relative to the air film and forming a first reflected light beam of the sampling light beam relative to the air film, b) guiding the first reflected light beam of the sampling light beam through the optical control subsystem to form a return light beam traveling in the opposite direction to the first reflected light beam, wherein the return light beam being incident to the specimen again at the the detecting site, therefore a second reflected light beam of the returned light beam is formed, while the second reflected light beam exits from the the optical control subsystem in the opposite direction to the the sampling light beam, it is to form a signal light beam, c) guiding the signal light beam through the analyzer and the detectors for detection of intensity and phase change of the signal light beam, d) partially dividing the signal light beam to form a observing light beam, which is guided to a microscope and used as a light source for observation of the detecting site on the the specimen, e) partially dividing the sampling light beam to form a reference light beam, which is guided to a reference light beam analyzer for measuring light intensity and phase change of the reference light beam as a calibration reference of non-linear phase retardation and non-uniform absorption in the phase modulator, and f) polarization state control method that utilizes intensity and phase change of the reference light beam as parameters to accurately control the polarization state of the sampling light beam.
Preferably, the transparent disk is a glass disk.
Preferably, the distance is to be measured less than one wavelength of the linear polarizing light.
Preferably, the slider is made of non-dielectric material.
Preferably, the slider is in static state relative to the transparent disk while the sampling light beam is incident onto a surface of the slider.
Preferably, the slider is in motion relative to the transparent disk while the sampling light beam is incident onto a surface of the slider.
Preferably, the incident light beam of the return light beam exits from the optical control subsystem to becomes a signal light beam traveling along the same path but in the opposite direction to the sampling light beam and at least twice reflecting from the detecting site.
Preferably, the observing light beam is used for the microscope as a light source of observation on detecting site as well as for the auto-collimation of the sampling light beam.
Preferably, control of polarization state of the sampling beam is done by a open-loop control.
Preferably, control of polarization state of the sampling beam is done by a close-loop control.
According to the third aspect of the present invention, the present invention is related to an apparatus for measuring the distance between a sliding object and a transparent disk with sub-nanometer resolution, wherein the distance is regarded as a nanometer specimen, at least comprising of a linear polarizing light source subsystem of which light intensity is to be tuned and initial linear polarization state is provided thereof to form a sampling light beam, a phase modulator for the control of phase change of the sampling light beam to vary initial polarization state of the linear polarizing light source, an optical control subsystem, which comprises a beam-bending element for guiding the sampling light beam incident to the detecting site in various angles, a carrier carrying and moving the the beam-bending element, and an optical component set comprising a focusing element and a normal reflection element, wherein the focusing element is used to guide the sampling light beam passing through the transparent disk to form a first reflected light beam at a detecting site of the specimen, and wherein the normal reflection element is used to normally reflect the first reflected light beam to form a return light beam traveling along the same path but in the direction opposite to the sampling light beam, therefore, a second reflected light beam of the return light beam at the detecting site is formed, while the second reflected light beam exits from the the optical control subsystem in the opposite direction to the the sampling light beam, it is to form a signal light beam, and a signal analysis subsystem for detecting light intensity and phase change of the signal light beam.
Preferably, the linear polarizing light source subsystem is simply a monochromatic, linear polarized light.
Preferably, the linear polarizing light source subsystem is composed of a diode laser and a linear polarizer.
Preferably, the linear polarizing light source subsystem further is composed of a light emitted diode (LED) and a linear polarizer.
Preferably, the phase modulator is a liquid crystal panel.
Preferably, the phase modulator is a photo-elastic phase modulator.
Preferably, the phase modulator is an optical compensator.
Preferably, the phase modulator is a half waveplate.
Preferably, the phase modulator is a quarter waveplate.
Preferably, the beam-bending element is a reflective mirror.
Preferably, the beam-bending element is a triangular prism.
Preferably, the beam-bending element is a penta prism.
Preferably, the carrier is a single-axis motion stage driven by a stepping motor.
Preferably, the carrier is a single-axis motion stage driven by a DC motor.
Preferably, the focusing element is a focusing mirror and the normal reflection element is a plane reflective mirror.
Preferably, the focusing element is a concave pseudo-paraboloidal mirror and the normal reflection element is a concave pseudo-spherical mirror.
Preferably, the signal analysis subsystem is composed of an analyzer and a photo detector.
According to the fourth aspect of the present invention, the present invention is related to an apparatus for measuring a distance between a sliding object and a transparent disk with sub-nanometer resolution, wherein the distance is regarded as a nanometer specimen, at least comprising of a linear polarizing light source subsystem of which light intensity is to be tuned and initial linear polarization state is provided thereof to form a sampling light beam, a phase modulator for the control of phase change of the sampling light beam to vary initial polarization state of the linear polarizing light source, an optical control subsystem, which comprises a beam-bending element for guiding the sampling light beam incident to the detecting site in various angles, a carrier carrying and moving the the beam-bending element, and an optical component set comprising a focusing element and a normal reflection element, wherein the focusing element is used to guide the sampling light beam passing through the transparent disk to form a first reflected light beam at a detecting site of the specimen, and wherein the normal reflection element is used to normally reflect the first reflected light beam to form a return light beam traveling along the same path but in the direction opposite to the sampling light beam, therefore, a second reflected light beam of the return light beam at the detecting site is formed, while the second reflected light beam exits from the the optical control subsystem in the opposite direction to the the sampling light beam, it is to form a signal light beam, a signal analysis subsystem for detecting light intensity and phase change of the signal light beam, a reference analysis subsystem for detection of light intensity and polarization state variation of the reference light beam and calibration of non-linear phase retardation and non-uniform absorption in the phase modulator to accurately control the polarization state of the sampling light beam, and a transfer function calibration device for detection of unknown ellipsometric parameters of the optical system.
Preferably, the linear polarizing light source subsystem is simply a monochromatic, linear polarized light.
Preferably, the linear polarizing light source subsystem is composed of a diode laser and a linear polarizer.
Preferably, the linear polarizing light source subsystem further is composed of a light emitted diode (LED) and a linear polarizer.
Preferably, the phase modulator is a liquid crystal panel.
Preferably, the phase modulator is a photo-elastic phase modulator.
Preferably, the phase modulator is an optical compensator.
Preferably, the phase modulator is a half waveplate.
Preferably, the phase modulator is a quarter waveplate.
Preferably, the beam-bending element is a reflective mirror.
Preferably, the beam-bending element is a triangular prism.
Preferably, the beam-bending element is a penta prism.
Preferably, the carrier is a single-axis motion stage driven by a stepping motor.
Preferably, the carrier is a single-axis motion stage driven by a DC motor.
Preferably, the focusing element is a focusing mirror and the normal reflection element is a plane reflective mirror.
Preferably, the focusing element is a concave pseudo-paraboloidal mirror and the normal reflection element is a concave pseudo-spherical mirror.
Preferably, the signal analysis subsystem is composed of an analyzer and a photo detector.
Preferably, the reference analysis subsystem is composed of an analyzer, a first photo detector and a second photo detector.
Preferably, the transfer function calibration device is a convex pseudo-spherical mirror.